Abstract: Obesity is multifactorial in origin. While energy imbalance is the proximal c# use of obesity, many factors influence energy imbalance. The genetically determined sensitivity to bitter taste (sensitivity to propylthiouracil (PROP)) has been inversely related to obesity among adults and to precursors of obesity (e.g. total energy) among young children. As a possible explanation for these relationships, PROP has also been inversely related to preferences for vegetables with a bitter taste, spicy foods (e g. capsaicin) and dietary fat intake. Thus, PROP sensitivity provides a genetically determined influence on behaviors which may lead to obesity among children. While there is a growing literature on PROP sensitivity in white adults, very little has been published among children or among ethnic minorities. It has not teen established whether this genetically determined trait is expressed at birth and remains constant through life, or if there are developmental influences on its expression. Early work on sensitivity to bitter tastes around the globe suggested large differences in this sensitivity across continents, and thereby ethnic groups. There; are no data, however, on whether the prevalence of PROP sensitivity differs by ethnic group in the US. Thus in one sample this research will assess the prevalence of PROP sensitivity among children in three age arid three ethnic groups, and assess the relationship of PROP sensitivity to adiposity status In a second sample, this research will also assess the relationship of PROP sensitivity to change in BMI over a 7 to 12 year period from 4 or 5 years of age to 12 to 16 years. In addition, both studies will test whether component; dietary intake mediate this relationship after controlling for energy expenditure and other possible confounding factors and whether psychosocial variables mediate the relationship of PROP status to FV intake. Knowing the prevalence of PROP sensitivity by age will specify possible differences in genetic expression by age. Differences in the prevalence by ethnic group could explain ethnic differences in obesity. Understanding how PROP sensitivity relates to obesity and food intake could provide an easily determined stratifying variable to which dietary interventions could be tailored.